Hydrogels have significant medical and pharmaceutical applications, particularly for contact-lens materials, drug-delivery vehicles, and artificial organs. This work is concerned with establishing a quantitative understanding of the properties of hydrogels in water which may contain biologically important solutes. Emphasis is directed at fundamental experimental and theoretical studies of hydrogel swelling and solute- partitioning behavior for guiding the design of novel materials that may find application in medicine and pharmacy. Novel hydrogels will be synthesized by copolymerizing 2-hydroxyethyl methacrylate (HEMA) with selected specialty comonomers; the added comonomers have been chosen to impart specific swelling and solute- partitioning behavior to the hydrogels. Swelling properties of these hydrogels will be measured as a function of the hydrogel structure (cross- link density, monomer concentration, comonomer concentration) and solution conditions (temperature, ionic strength, pH, solute concentration). Solute partitioning will be measured for a series of solutes at varying hydrogel and solution conditions. Model solutes have been chosen to cover a range of molecular weight and chemical constitution. Attention will be given to model solutes whose partitioning behavior is of interest in biomedical applications of hydrogels. A molecular-thermodynamic model will be established for relating hydrogel swelling and solute-partitioning behavior to hydrogel, solute, and solution properties. Preliminary results suggest that conventional models for hydrogel elasticity cannot describe swelling behavior as a function of monomer concentration. Mechanical measurements of hydrogel-network elasticity will be performed to provide data that will aid in applying new elasticity theories to hydrogel systems. To understand how microstructure affects hydrogel performance in solution, transmission electron microscopy will be used to observe hydrogel microstructure as a function of hydrogel chemistry and composition. Structure-property relationships inferred from microstructure observations will aid in model development. This research will provide fundamental physico-chemical information of the properties of hydrogels, and on the interactions of these hydrogels with aqueous solutions of medically important solutes. This information will aid in the design and development of novel hydrogel materials for applications in medicine and pharmacy.